LEDs have been increasingly adopted as light sources of headlights and taillights of automobiles, and the like. Because LEDs can be made to flash at high speed, a system performing communication so as to superimpose desired signal information onto flashing of an LED has been researched. For example, an inter vehicle communication system and a road to vehicle communication system using LEDs have been studied.
With respect to these communication systems, an optical communication device is described in Patent Document 1. The optical communication device performs communication by use of light onto which signals are superimposed. This optical communication device includes a solid state image pick-up device including pixels acquiring image signals, and pixels acquiring communication signals. Solid state image pick-up devices are described in Non-Patent Documents 1 and 2. These solid state image pick-up devices are configured to be capable of detecting a communication signal and an image signal. A CMOS solid state image pick-up device is described in Non-Patent Document 3. This solid state image pick-up device is improved in response characteristics with respect to light onto which signals are superimposed. This solid state image pick-up device includes a structure of causing a photodiode to perform an incomplete accumulation operation, and a structure of detecting an electric charge having extremely small capacitance. In accordance with the solid state image pick-up device including these structures, it is possible to achieve a transmission rate of 10 Mbps in an outdoor environment.